"vErE spErO tE eA quA dEbEbis dIligentiA hoc opus factUrum" with the capitalized vowels being the ones that have macrons over them

So I understand it to mean

I truly hope that you are going to do this work.....eA quA dEbEbis dIligentiA

with this diligence which you owe?

eA dIligentiA makes sense to me as the ablative of manner, but what i do not understand is quA dEbEbis

it seems like it is a subordinate clause introduced by a relative pronoun, but why is quA ablative, and why is dEbEbis future indicative? I thought that verbs in subordinate clauses in indirect statements took the subjunctive, and i do not believe that I recall anything about debeo taking the ablative...

its adapted from pliny's letter #38 to trajan, though i'm not translating the work, its just a homework sentence

I'm a little less sure on the future indicative, but my understanding is that you keep the indicative in indirect statements when the subordinate clause is independent of the indirect discourse, so in this case this diligence that he will have to have is diligence he will have to have irrespective of what the speaker might hope for him to do. It seems to me in these cases that English simply doesn't really make that distinction. For this there's the section on subordinate clauses at http://books.google.ca/books?id=DLMAAAA ... 1-PA372,M1